1. Field of the Invention
The present invention relates to "Bendix" type starters for starting internal combustion engines of motorcycles and the like. More particularly, the invention relates to a starter device provided with means for preventing premature retreat of the pinion gear thereof at an initial unstable stage of the internal combustion engine when it is started.
2. Description of Relevant Art
A "Bendix" drive or "inertial" type starter is well known in the art for use as a device for starting an internal combustion engine of a motorcycle or other vehicle. Such type of starter comprises a pinion gear fitted on a pinion shaft rotated by a starter motor and a movable cylindrical member coupled to the pinion gear through a unidirectional clutch, the movable cylindrical member being fitted on the pinion shaft and coupled thereto by a helical spline coupling. When the pinion shaft is rapidly rotated by the starter motor, the movable cylindrical member and pinion gear are caused to move or slide along the pinion shaft due to their inertia, and the pinion gear is brought into mesh with a ring gear of the engine as the pinion gear reaches the end of the pinion shaft. As a result, the ring gear is rotated by the pinion gear, to thus start the engine. After the engine has been started, the unidirectional clutch permits free rotation of the pinion gear relative to the movable cylindrical member. When the rpm (revolutions per minute) of the pinion gear is increased beyond that of the pinion shaft with forced torque received from the ring gear and reaches a predetermined rpm, the pinion gear and movable cylindrical member are retreated along the pinion shaft by dragging torque of the unidirectional clutch and a spring force of a return spring, so that the ring gear is released from the pinion gear.
It is known that the engine does not reach a stable running condition immediately after ignition. During a certain initial period after starting the engine, the rpm fluctuates and momentarily reaches a rpm at which the pinion gear is permitted to be detached from the ring gear. Accordingly, there has been known a device in which the premature releasing of the meshing engagement between the pinion gear and ring gear is prevented by a detachment-prevention member such as a slide pin until the condition of the engine is stable, with a constant rpm. This type of device, however, is unsatisfactory and indeed substantially infeasible for single-cylinder engines or two-cycle engines of motorcycles and the like, the rpm of which fluctuates considerably.
When the pinion gear is detached from the ring gear and prematurely retreated due to fluctuations of the rpm of the engine during the initial unstable stage thereof, before reaching its stable running condition, an igniter malfunctions, and the engine is consequently stopped. Such condition is shown in FIG. 9 in the form of a graph, wherein the ordinate represents the rpm (N), and the abscissa represents the time (T). During the initial stage after starting the engine, the rpm thereof fluctuates in a wavy fashion, and the rpm of the pinion gear similarly fluctuates as shown in the graph and momentarily reaches a high rpm A. The pinion shaft is rotated at a rpm B which is determined by the starter motor. When the rpm of the pinion gear afforded by the ring gear exceeds the rpm of the pinion shaft as such rpm of the pinion gear momentarily reaches the high value A, a force tending to detach and retreat the pinion gear from the ring gear is produced due to dragging torque provided by the unidirectional clutch, thus causing premature detachment of the pinion gear from the ring gear before the engine has reached its stable running condition. Therefore, a failure in ignition results which causes the engine to stop. In such event, it is necessary to stop the starter motor once and operate a switch therefor again, which operation is time-consuming and inconvenient.
The aforesaid problem may be solved by employing a starter motor wherein the rpm B of the pinion shaft is always higher than the momentary peak rpm A of the pinion gear, even if the rpm of the engine fluctuates. However, such a starter motor requires a high torque, a high capacity, and high rpm ratings, which necessitates a larger size of the starter motor. Accordingly, such a starter motor is highly undesirable from the standpoint of the demand for reducing the size of starter motors.
Another important aspect of achieving reliable performance of the "Bendix" type starter is to ensure that the pinion gear moves smoothly along the pinion shaft. The various components of the starter, including the pinion gear and movable cylindrical member, are assembled in a case filled with lubricating oil. At some time in the course of repeated use of the starter over a long period of time, dust eventually drops into the lubricating oil. The contained dust attaches itself to the surface of the pinion shaft and obstructs the frictional movement of the pinion gear. Also, if dust intrudes into the gap between the pinion gear and pinion shaft, smooth movement of the pinion gear is impeded, and in extreme cases the engine can no longer be started. Thus, it is necessary to guarantee smooth frictional movement of the pinion gear along the pinion shaft without being adversely affected by dust.
The present invention effectively overcomes the above-described problems inherent in known starter constructions.